The Children's Cancer Center at St. Louis Children's Hospital is the only such center within a 200 mile radius which offers multimodal therapy to children with malignant disease, regardless of ability to pay. Twenty percent of the 200 patient pediatric oncology census is totally medically indigent and most of the rest can afford to pay only part of the charges. At the time of diagnosis of a malignancy in a child, the clinical findings are reviewed and management is discussed at the weekly pediatric tumor conference by the pediatric oncologists, radiation therapists, surgeons, and pathologists, in order to assure that each child receives optimal therapy. Access to new intensive multimodal therapeutic regimens and experimental compounds is facilitated by the collaboration of the Center with the Southwest Oncology Group. Extensive ancillary studies, both at the clinical and preclinical levels, are underway in parallel with the oncology studies in children. The spleen colony assay technique is being used to quantitate the effects of different doses and schedules of combination chemotherapy, with or without radiation therapy, on malignant cells and normal hematopoietic stem cells. Parallel in vitro studies are being done. Similar in vitro and animal in vivo studies are in the process of elucidating that humoral immunostimulation may be a factor in modulating the growth of nascent tumors. Results from these preclinical studies are presently being applied to scheduling of combination chemotherapy in children, with the hope that a more rational basis for therapy, and thus more effective therapy, will evolve.